Coatings for gaskets often serve not only for protecting the coated materials from weathering and similar effects, but also for improving the sealing properties of the gasket. This presupposes, in particular, a high capacity of the coating to adapt to the mating surface that is to be sealed off, and in this way, to be able to counteract areas of roughness or unevenness in the mating surface. The coating has to have high deformability for this purpose.
However, there are also cases in which, in addition to a good capacity to adapt to the mating surface, good long-term sliding capability properties on the mating surface are also desired. However, good long-term sliding properties presuppose low flow properties of the coating along with low deformability, i.e., properties that run counter to a good capacity of the coating to adapt to the mating surface.
An example of a gasket which is required to have good long-term sliding properties and a high capacity of adapting to the mating surfaces which are to be sealed off is a cylinder head gasket. Until recently, cylinder head gaskets were usually provided with a thin coating with a thickness of perhaps a few micrometers, whereby this is intended to improve the capacity of the gasket to adapt to the areas of unevenness and roughness of the mating surfaces (engine block and cylinder head) which are to be sealed off.
Such conventional coatings comprise, e.g., nonvulcanized rubber, soft metals or molybdenum disulfide. These coatings certainly improve the capacity of the cylinder head gasket to adapt to the mating surfaces, but they are not satisfactory in terms of long-term sliding properties. Conventional coatings, rather, flow laterally into regions in which they are exposed to particularly high surface pressure so that, after a certain running time, the cylinder head gasket in these regions comes directly into contact with the mating surface that is to be sealed off.
A demand therefore existed for a coating that mutually combines a good capacity to adapt to the mating surface which is to be sealed off, with good long-term sliding properties, on the one hand, and on the other hand maintains these properties even at a high surface pressure and a high temperature.